Just a day after the Bureau of Meteorology extended its palette range to cope with the country’s unprecedented heatwave, the zones of purple — representing 50-52 degrees — have disappeared from forecast charts for the next few days.

Purple vanishes in the haze ... the new Bureau of Meteorology's interactive weather forecasting.

Weather projections made more than a few days out are, by their nature, less reliable, said Aaron Coutts-Smith, NSW manager for climate services at the bureau.

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Predictions on Tuesday by the bureau’s model that parts of the inland would exceed 50 degrees next Sunday and Monday were "a little too emphatic", he said on Wednesday.

That’s not to say Australia’s massive heatwave is showing much sign of cresting — and the colour scheme remains an option if the mercury breaks the 50-degree point at any of the bureau's sites.

Deep purple ... the Bureau of Meteorology's interactive weather forecasting chart added new colours but they have since disappeared.

The country posted a record average maximum on Monday of 40.33 degrees and although the latest indications suggest Tuesday’s tally fell short of setting a new peak, at 40.11 degrees it was the third-highest ever. The national mean temperature, though, shattered the previous record - which had stood for 40 years - on Monday and broke it again on Tuesday.

And while coastal areas, particularly in the south-east will see some relief to the extreme heat and fire conditions, the giant heat cell over central Australia has days to run.

“We’re not anticipating any significant clearing of that hot air,” Dr Coutts-Smith said.

Forecasters expect Sunday and Monday to provide the next chance of 50-plus degrees — and for the possible appearance of that new purple shade to the country’s observed weather charts, not just the forecast maps.

Ben McBurney, a meteorologist at Weatherzone, says outback towns ranging from Bourke and Cobar in NSW to Moomba, Oodnadatta and Marree in South Australia are all candidates to reach 50 degrees in coming days.

“There’s potential for Bourke to reach 48-49 degrees and may get to 50 degrees on Sunday or Monday,” Mr McBurney said, “which is quite scary when you think of it.”

For now, the weather bureau is taking a more conservative approach, with Bourke predicted to hit 45, 46, and 46 degrees on Friday, Saturday and Sunday, respectively, before easing back to a maximum of 42 on Monday.

Other high temperature forecasts from the bureau include 48 on Sunday for Moomba and Marree.

Australia's record maximum is 50.7 degrees reached at Oodnadatta Airport on January 2, 1960, while the highest for NSW was set at Menindee Post Office on January 10, 1939 at 49.7 degrees.